Emulsifier-free finely disperse systems of the oil-in-water and water-in-oil type

ABSTRACT

Pickering emulsions, which are finely disperse systems of the water-in-oil or oil-in-water type, comprising
     (1) an oil phase,   (2) a water phase,   (3) at least one type of microfine particles which
       a) have an average particle size of less than 200 nm, which   b) display both hydrophilic and lipophilic properties, i.e. which have amphiphilic character, and are dispersible both in water and in oil and which   c) have optionally been coated on the surface,   
       (4) at least one electrolyte and   (5) at most 0.5% by weight of one or more emulsifiers.

This application is a divisional of U.S. application Ser. No. 09/388,717, filed on 2 Sep. 1999, now U.S. Pat. No. 6,585,983.

The present invention relates to emulsifier-free finely disperse systems of the oil-in-water and water-in-oil type, preferably as cosmetic or dermatological preparations.

Emulsions are generally taken to mean heterogeneous systems which consist of two liquids which are immiscible or have only limited miscibility with one another, which are usually referred to as phases. In an emulsion, one of the two liquids is dispersed in the form of very fine droplets in the other liquid.

If the two liquids are water and oil and if oil droplets are finely dispersed in water, then this is an oil-in-water emulsion (O/W emulsion, e.g. milk). The basic character of an O/W emulsion is defined by the water. In a water-in-oil emulsion (W/O emulsion, e.g. butter), the principle is reversed, the basic character here being determined by the oil.

In order to achieve permanent dispersion of one liquid in another, emulsions in the traditional sense require the addition of an interface-active substance (emulsifier). Emulsifiers have an amphiphilic molecular structure, consisting of a polar (hydrophilic) and a nonpolar (lipophilic) molecular moiety, which are spatially separate from one another. In simple emulsions, finely disperse droplets of one phase, surrounded by an emulsifier shell, (water droplets in W/O emulsions or lipid vesicles in O/W emulsions) are present in the second phase. Emulsifiers lower the interfacial tension between the phases by positioning themselves at the interface between two liquids. At the phase boundary, they form oil/water interfacial films, which prevent irreversible coalescence of the droplets. Emulsions are frequently stabilized using emulsifier mixtures.

Traditional emulsifiers can, depending on their hydrophilic molecular moiety, be divided into ionic (anionic, cationic and amphoteric) and nonionic:

-   -   The most well-known example of an anionic emulsifier is soap,         which is usually the term used for the water-soluble sodium or         potassium salts of saturated or unsaturated higher fatty acids.     -   Important examples of cationic emulsifiers are quaternary         ammonium compounds.     -   The hydrophilic molecular moiety of nonionic emulsifiers         frequently consists of glycerol, polyglycerol, sorbitans,         carbohydrates and polyoxyethylene glycols, and, in most cases,         is linked to the lipophilic molecular moiety via ester and ether         bonds. The lipophilic molecular moiety usually consists of fatty         alcohols, fatty acids or isofatty acids.

By varying the structure and the size of the polar and nonpolar molecular moiety, the lipophilicity and hydrophilicity of emulsifiers can be varied within wide limits.

A decisive factor for the stability of an emulsion is the correct choice of emulsifiers. The characteristics of all substances present in the system are to be taken into consideration here. In the case of, for example, skincare emulsions, polar oil components and, for example, UV filters lead to instability. As well as the emulsifiers, therefore, other stabilizers are also used which, for example, increase the viscosity of the emulsion and/or act as protective colloid.

Emulsions are an important type of product in the field of cosmetic and/or dermatological preparations.

Cosmetic preparations are essentially used for skin care. The main aim of skin care in the cosmetics sense is to strengthen or rebuild the skin's natural function as a barrier against environmental influences (e.g. dirt, chemicals, microorganisms) and against the loss of endogenous substances (e.g. water, natural fats, electrolytes). If this function becomes impaired, increased resorption of toxic or allergenic substances or attack by microorganisms may result, leading to toxic or allergic skin reactions.

Another aim of skin care is to compensate for the loss by the skin of lipids and water caused by daily washing. This is particularly important if the natural regeneration ability is inadequate. Furthermore, skincare products should protect against environmental influences, in particular against sun and wind, and delay skin ageing.

Cosmetic preparations are also used as deodorants. Such formulations are used to control body odour, which is produced when fresh perspiration, which is in itself odourless, is decomposed by microorganisms.

Medicinal topical compositions usually comprise one or more medicaments in an effective concentration. For the sake of simplicity, in order to distinguish clearly between cosmetic and medicinal use and corresponding products, reference is made to the legal provisions in the Federal Republic of Germany (e.g. Cosmetics Directive, Foods and Drugs Act).

The use of customary emulsifiers in cosmetic or dermatological preparations is in itself acceptable. Nevertheless, emulsifiers, like ultimately any chemical substance, may in certain circumstances cause allergic reactions or reactions based on oversensitivity of the user.

For example, it is known that certain light dermatoses are triggered by certain emulsifiers, but also by various fats and simultaneous exposure to sunlight. Such light dermatoses are also called “Mallorca acne”. There has thus been no lack of attempts to reduce the amount of customary emulsifiers to a minimum, in the ideal case even to zero.

A reduction in the required amount of emulsifier can, for example, be achieved by taking advantage of the fact that very finely divided solid particles have an additional stabilizing action. The solid substance accumulates at the oil/water phase boundary in the form of a layer, as a result of which coalescence of the disperse phases is prevented. It is not the chemical properties of the solid particles which are of fundamental importance here, but the surface properties.

Around 1910, Pickering prepared paraffin/water emulsions which were stabilized merely by the addition of various solids, such as basic copper sulphate, basic iron sulphate or other metal sulphates. This type of emulsion is thus also referred to as a Pickering emulsion.

The original forms of Pickering emulsions initially surfaced, as it were, as undesired secondary effects in a variety of industrial processes, such as, for example, in secondary oil recovery, the extraction of bitumen from tar sand and other separation processes involving two immiscible liquids and fine, dispersed solid particles. These are generally W/O emulsions which are stabilized by mineral solids. Accordingly, investigation of corresponding systems, such as, for example, the oil/water/soot or oil/water/slate dust systems was initially the focus of research activity.

Basic experiments have shown that one characteristic of a Pickering emulsion is that the solid particles are arranged at the interface between the two liquid phases, where they form, as it were, a mechanical barrier against the combining of the liquid droplets.

It is a relatively new technical development to use Pickering emulsions as a base for cosmetic or dermatological preparations.

One way of achieving solids stabilization in the sense of a pickering emulsion in a cosmetic or dermatological preparation is, according to May-Alert (Pharmazie in unserer Zeit [Pharmacy in our time], Vol. 15, 1986, No. 1, 1–7) for example, to use emulsifier mixtures which comprise both anionic and cationic surfactants. Since mixing anionic and cationic surfactants always results in the precipitation of insoluble, electroneutral compounds, deliberate precipitation of these neutral surfactants in the oil/water interface makes it possible to achieve additional solids stabilization.

European Laid-open Specification 0 686 391, moreover, describes emulsions of the water-in-oil type which are free from surface-active substances and are stabilized only by solids. Stabilization is achieved here using spherical polyalkylsilsesquioxane particles which have a diameter of from 100 nm up to 20 μm. These emulsions can be referred to as Pickering emulsions according to that mentioned above.

Pickering emulsions are stabilized by the use of suitable solids or pigments. However, the preparations of the prior art generally have the disadvantage that they are limited to a narrow field of application or a restricted choice of starting materials since they can only be stably formulated in this manner. For many areas of cosmetics (e.g. for the field of face care), Pickering emulsions of the prior art have unsatisfactory cosmetic properties.

The object was therefore to remedy the disadvantages of the prior art. In particular, the intention was to provide cosmetic and dermatological bases for cosmetic and dermatological preparations which are characterized by good skin tolerability.

In addition, an object of the present invention was to provide products with the widest possible variety of applications. For example, the intention was to provide bases for preparation forms such as cleansing emulsions, facecare and bodycare preparations or deodorants, but also distinctly medicinal-pharmaceutical presentations, for example preparations against acne and other skin conditions.

It was surprising and in no way predictable by the person skilled in the art that Pickering emulsions, which are finely disperse systems of the water-in-oil or oil-in-water type, comprising

-   (1) an oil phase, -   (2) a water phase, -   (3) at least one type of microfine particles which     -   a) have an average particle size of less than 200 nm, which     -   b) display both hydrophilic and lipophilic properties, i.e.         which have amphiphilic character, and are dispersible both in         water and in oil and which     -   c) have optionally been coated on the surface, -   (4) at least one electrolyte and -   (5) at most 0.5% by weight of one or more emulsifiers,     overcome the disadvantages of the prior art.

According to the invention, it is particularly advantageous if the preparations comprise significantly less than 0.5% by weight of one or more emulsifiers or are even entirely free from emulsifiers.

The preparations according to the invention are extremely satisfactory preparations in every respect which have considerably higher stability compared with traditional Pickering emulsions and are therefore suitable in particular to serve as bases for preparation forms having diverse application purposes. In particular, W/O Pickering emulsions within the meaning of the present invention are, surprisingly, markedly stable.

In addition, the preparations according to the invention are characterized by excellent skin tolerability. In addition, it was surprising that preparations according to the invention, which are in the form of a sunscreen, exhibit higher effectiveness than customary sunscreen formulations.

While preparations of the prior art having a pigment content of as little as 1% by weight produce a dull feel following their application to the skin, which increases further with higher pigment concentrations, the preparations according to the invention, surprisingly, do not leave a dry or dull impression on the skin, but on the contrary exhibit excellent cosmetic properties.

Although the prior art recognizes, in addition to Pickering emulsions, emulsifier-free, finely disperse cosmetic or dermatological preparations, which are generally referred to as hydrodispersions and which are dispersions of a liquid, semisolid or solid inner (discontinuous) lipid phase in an outer aqueous (continuous) phase, the prior art was unable to point the way to the present invention.

In the case of hydrodispersions of a liquid lipid phase in an external aqueous phase, the stability can be guaranteed, for example, by building up a gel structure in the aqueous phase, in which the lipid droplets are stably suspended.

German Laid-Open specification 44 25 268 describes stable finely disperse, emulsifier-free cosmetic or dermatological preparations of the oil-in-water type, which in addition to an oil and a water phase contain one or more thickeners from the group consisting of the acrylic acid polymers, polysaccharides and their alkyl ethers, where a lowering of interfacial tension must not be measurable for these thickeners.

Based on similar hydrodispersions, German Laid-Open specification 43 03 983 discloses cosmetic or dermatological sunscreen formulations which are essentially free of emulsifiers, the hydrodispersion of inorganic micropigments which serve as UV filter substances being incorporated into the lipid phase.

O/W Pickering emulsions within the meaning of the present invention, however, are obtainable by first dispersing amphiphilic particles according to the invention which are suitable for the preparation of O/W Pickering emulsions in the water phase and then combining the water phase with the fatty phase. W/O Pickering emulsions according to the invention, however, are obtainable by dispersing amphiphilic particles according to the invention which are suitable for the preparation of W/O Pickering emulsions in the fatty phase.

According to the invention, the electrolyte(s) is/are advanatgeously selected from the group consisting of

-   (1) the salts with the following anions: chlorides, furthermore     inorganic oxo element anions, of these in particular sulphates,     carbonates, phosphates, borates and aluminates. Electrolytes based     on organic anions are also advantageous, e.g. lactates, acetates,     benzoates, propionates, tartrates, citrates, amino acids and their     salts and many others. Comparable effects can also be achieved by     means of ethylenediaminetetraacetic acid and its salts.     -   Cations of the salts preferably used are ammonium,         alkylammonium, alkali metal, alkaline earth metal, magnesium,         iron and zinc ions. It does not need mentioning per se that only         physiologically acceptable electrolytes should be used in         cosmetics. Potassium chloride, sodium chloride, magnesium         sulphate, zinc sulphate and mixtures thereof are particularly         preferred.

According to the invention, the electrolyte(s) is/are furthermore advantageously selected from the group (2), which comprises:

-   (2) certain water-soluble UV filter substances which are mostly     present as alkali metal salts, in particular those which carry one     or more sulphonic acid groups or sulphonate groups in their     molecular structure:     -   2-phenylbenzimidazole-5-sulphonic acid and its salts, for         example the sodium or potassium salt or its triphenolammonium         salt     -   sulphonic acid derivatives of benzophenones, preferably         2-hydroxy-4-methoxybenzophenone-5-sulphonic acid and its salts,         for example the corresponding sodium, potassium or         triphenolammonium salt:     -   sulphonic acid derivatives of 3-benzylidenecamphor, such as, for         example, 4-(2-oxo-3-bornylidenemethyl)benzenesulphonic acid and         its salts, for example the corresponding sodium, potassium or         triethanolammonium salt:     -   2-methyl-5-(2-oxo-3-bornylidenemethyl)benzenesulphonic acid and         its salts, for example the corresponding sodium, potassium or         triethanolammonium salt:     -   1,4-di(2-oxo-10-sulpho-3-bornylidenemethyl)benzene and its salts         (the corresponding 10-sulphato compounds, for example the         corresponding sodium, potassium or triethanolammonium salt),         also referred to as         benzene-1,4-di(2-oxo-3-bornylidenemethyl-10-sulphonic acid:

According to the invention, the electrolyte(s) is/are furthermore advantageously selected from the group consisting of

-   (3) the amino acids and their salts or their anions. Amino acids are     a constituent of the natural moisturizing factor. The addition of     amino acids, in particular of essential amino acids, is to be     regarded as advantageous, since moisture can be bound up in the skin     by means of hydration processes.     -   Amino acids having a particularly advantageous cosmetic or         dermatological action are glycine, alanine, valine, leucine,         isoleucine, phenylalanine, tyrosine, proline, hydroxyproline,         serine, threonine, cysteine, methionine, tryptophan and         arginine.

According to the invention, the electrolyte(s) is/are further advantageously selected from the group consisting of

-   (4) the cosmetically and dermatologically relevant     α-hydroxycarboxylic acids, α-ketocarboxylic acids and     β-hydroxycarboxylic acids and in particular their salts, where the     cations can advantageously be selected from the group consisting of     ammonium, alkylammonium, alkali metal, alkaline earth metal,     magnesium, iron and zinc ions.     -   α-Hydroxycarboxylic acids which are cosmetically or         dermatologically relevant obey the general formula     -   β-Hydroxycarboxylic acids which are cosmetically or         dermatologically relevant obey the general formula     -   α-Ketocarboxylic acids which are cosmetically or         dermatologically relevant obey the general formula     -   where in each case R′ and R″ independently of one another are         selected from the groups     -   (a1) H,     -   (a2) branched or unbranched C₁₋₂₅-alkyl,     -   (a3) branched or unbranched C₁₋₂₅-alkyl substituted by one or         more carboxyl groups and/or hydroxyl groups and/or aldehyde         groups and/or oxo groups (keto groups),     -   (a4) phenyl,     -   (a5) phenyl substituted by one or more carboxyl groups and/or         hydroxyl         -   groups and/or branched and/or unbranched C₁₋₂₅-alkyl groups,     -   or where the α-carbon atom and the β-carbon atom of the         β-hydroxycarboxylic acid with R′ and R″ together form an     -   (a6) unsubstituted cycloalkyl group or aryl group having 3 to 7         ring atoms or a     -   (a7) cycloalkyl group or aryl group having 3 to 7 ring atoms         substituted by one or more carboxyl groups and/or hydroxyl         groups and/or oxo groups (keto groups) and/or branched and/or         unbranched C₁₋₂₅-alkyl groups and     -   where the α-hydroxycarboxylic acids or the β-hydroxycarboxylic         acids or the α-ketocarboxylic acids can optionally be present in         the form of their physiologically tolerable salts.

α-Hydroxycarboxylic acids, β-hydroxycarboxylic acids and α-ketocarboxylic acids advantageously to be used in the context of the present invention follow, these also being mentioned as representing their salts or anions:

-   salicylic acid (also 2-hydroxybenzoic acid), which is characterized     by the structure

As is known, salicylic acid has an antibacterial and keratolytic action and is a constituent of some cosmetic or pharmaceutical preparations.

The α-hydroxycarboxylic acids according to the invention are advantageously selected from the following substance classes:

-   (b1) α-hydroxy fatty acids, these in turn being particularly     advantageously selected from the group consisting of the     C₁₀₋₁₈-alkylcarboxylic acids, -   (b2) α-hydroxy sugar acids, aliphatic α-hydroxy fruit acids, -   (b3) unsubstituted aromatic α-hydroxycarboxylic acids (e.g. madelic     acid) and -   (b4) substituted aromatic α-hydroxycarboxylic acids.

The α-hydroxy fatty acids coming under (b1) are particularly advantageously selected from the group consisting of

-   -   α-hydroxycarboxylic acids, according to the formula     -   α-hydroxyisocarboxylic acids, according to the formula     -   α-hydroxyanteisocarboxylic acids, according to the formula         where n in each case is a number smaller than 7.

It is furthermore advantageous to use mixtures of such aliphatic α-hydroxycarboxylic acids, in particular in the form of wool wax acid mixtures in which the content of α-hydroxycarboxylic acids is 20 to 30% by weight, based on the total composition.

The α-hydroxy sugar acids coming under item (b2) are particularly advantageously selected from the group consisting of the

-   -   aldonic acids, e.g. gluconic acid, galactonic acid     -   aldaric acids, e.g. glucaric acid, galactaric acid (but also the         fruit acid tartaric acid, which likewise comes under the         definition of aldaric acid)     -   uronic acids, e.g. glucuronic acid, galacturonic acid     -   glyceric acid

The aliphatic α-hydroxy fruit acids coming under item (b2) are particularly advantageously selected from the group consisting of malic acid, lactic acid, citric acid and tartaric acid.

Malic acid (hydroxysuccinic acid) is characterized by the following chemical structure:

Lactic acid (2-hydroxypropanoic acid) is characterized by the following chemical structure:

Citric acid (2-hydroxy-1,2,3-propanetricarboxylic acid) is characterized by the following chemical structure:

As is known, citric acid is used for buffering cosmetic and/or dermatological preparations, but also as a synergist for antioxidants in skin and hair cosmetics.

Tartaric acid (dihydroxysuccinic acid) is characterized by the following chemical structure:

The preferred α-ketocarboxylic acid is pyruvic acid (α-oxypropanoic acid). It is distinguished by the following structure:

The total amount of one or more electrolytes in the finished cosmetic or dermatological preparations is advantageously selected to be less than 5% by weight, preferably between 0.5 and 2.0% by weight, based on the total weight of the preparations.

It is particularly preferred within the meaning of the present invention to stabilize W/O Pickering emulsions by the addition of electrolytes according to the invention.

It is also advantageous, although not obligatory, for the Pickering emulsions according to the invention to comprise other auxiliaries which can additionally increase the stability of these preparations, for example substances which are chosen from the group of waxes and/or oil thickeners, and of hydrocolloids.

It is also advantageous for the Pickering emulsions according to the invention to comprise auxiliaries which can contribute to reducing or preventing a dull or dry feel on the skin following their application, where it is possible that the main purpose of these substances is a different one. Preferably, these substances are, for example, chosen from the group of unsymmetrically substituted s-triazine derivatives, cyclodextrins, film formers and polymeric moisturizers, it being possible for these substances to be present either individually or in a mixture.

The cosmetic properties of the Pickering emulsions according to the invention can additionally, for example, be further improved by also using oils in the oil phase which have a viscosity of less than 30 mPa.s, in particular of less than 20 mPa.s (determined using a rheometer from Contraves (Rheomat 108E) at a shear gradient of 500/s and a temperature of 25° C.).

Microfine Particles:

The amphiphilic character of the microfine particles according to the invention is evident, for example, from the fact that they are dispersible both in water and in oil.

It is advantageous to choose the average particle diameter of the particles used to be between 1 nm and 200 nm, particularly advantageously between 5 nm and 100 nm.

It is also advantageous to choose the concentration of all amphiphilic particles according to the invention to be greater than 0.1% by weight, particularly advantageously between 0.1% by weight and 30% by weight, based on the total weight of the preparations.

For the purposes of the present invention, advantageous particles are all those which are suitable for stabilizing Pickering W/O emulsions or Pickering O/W emulsions. It is essentially insignificant for the present invention in which of the potentially naturally occurring modifications the particles are present.

To stabilize the Pickering emulsions, preference is given to using untreated, virtually pure pigment particles, in particular those which can be used as dyes in the food industry and/or as absorbers of UV radiation in sunscreens. Examples of advantageous pigments are the zinc oxide pigments available from Merck which are available under the trade names Zinkoxid neutral from Haarmann & Reimer or NanoX from Harcros Chemical Group.

For the purposes of the present invention, Pickering emulsions are likewise advantageously stabilized by inorganic pigments which have been surface-treated (“coated”) to repel water, where at the same time the intention is to form or retain the amphiphilic character. This surface-treatment can consist in providing the pigments with a thin hydrophobic layer by processes known per se.

One such process, which is described below using titanium dioxide as an example, consists in, for example, producing the hydrophobic surface layer according to the following reaction n TiO₂ +m (RO)₃Si—R′→n TiO₂ (surf.).

n and m are arbitrary stoichiometric parameters, and R and R′ are the desired organic radicals. Particularly advantageous are TiO₂ pigments, for example those coated with aluminium stearate, available under the trade name MT 100 T from TAYCA.

A further advantageous coating of the inorganic pigments consists of dimethylpolysiloxane (also: dimethicone), a mixture of completely methylated, linear siloxane polymers which are terminally blocked with trimethylsiloxy units. For the purposes of the present invention, particularly advantageous pigments are zinc oxide pigments which are coated in this way.

Also advantageous is a coating of the inorganic pigments with a mixture of dimethylpolysiloxane, in particular dimethylpolysiloxane having an average chain length of from 200 to 350 dimethylsiloxane units, and silica gel, which is also referred to as simethicone. It is particularly advantageous if the inorganic pigments have been additionally coated with aluminium hydroxide or hydrated aluminium oxide (also: alumina, CAS No. 1333-84-2). Particularly advantageous are titanium dioxides which have been coated with simethicone and alumina, it being possible for the coating to also comprise water. One example thereof is the titanium dioxide available under the trade name Eusolex T2000 from Merck.

For the purposes of the present invention it is also advantageous to use a mixture of different pigment types either within a crystal, for example as mixed iron oxide, or by combination of two or more pigment types within a preparation.

The Pickering emulsions are also preferably stabilized by boron nitride particles, for example by the boron nitrides listed below:

Trade name Available from Boron Nitride Powder Advanced Ceramics Boron Nitride Powder Sintec Keramik Ceram Blanche Kawasaki HCST Boron Nitride Stark Très BN ® Carborundum Wacker-Bornitrid BNP Wacker-Chemie

It is advantageous to choose the average particle diameter of the boron nitride particles used to be less than 20 μm, particularly advantageously less than 15 μm. For the purposes of the present invention, Pickering emulsions are likewise advantageously stabilized by boron nitride particles which have been surface-treated (“coated”) to repel water, where at the same time the intention is to form or retain the amphiphilic character.

An advantageous coating of the boron nitride particles consists of dimethylpolysiloxane (dimethicone). The boron nitride particles treated with dimethicone and available from Carborundum under the trade name Très BN® UHP 1106 are advantageous, for example.

Also advantageous is a coating of the boron nitride particles with polymethylhydrogensiloxane, a linear polysiloxane which is also referred to as methicone. Advantageous boron nitride particles treated with methicone are, for example, those available from Carborundum under the trade name Très BN® UHP 1107.

It is also advantageous to stabilize the Pickering emulsions according to the invention using microfine polymer particles.

For the purposes of the present invention, examples of advantageous microfine polymer particles are polycarbonates, polyethers, polyethylenes, polypropylenes, polyvinyl chloride, polystyrene, polyamides, polyacrylates and the like.

Advantageous according to the invention are, for example, microfine polyamide particles which are available under the trade name SP-500 from TORAY. Also advantageous are polyamide 6 (also: nylon 6) and polyamide 12 (also: nylon 12) particles. Polyamide 6 is the polyamide formed from ε-aminocaproic acid (6-aminohexanoic acid) or ε-caprolactam [poly(ε-caprolactam)], and polyamide 12 is a poly(ε-laurolactam) from ε-laurolactam. For the purposes of the present invention, Orgasol® 1002 (polyamide 6) and Orgasol® 2002 (polyamide 12) from ELF ATOCHEM, for example, are advantageous.

Other advantageous polymer particles are microfine polymethacrylates. Such particles are available, for example, under the trade name POLYTRAP® from DOW CHEMICAL.

It is particularly advantageous, but not obligatory, if the microfine polymer particles used have been surface-coated. This surface-treatment can consist in providing the pigments with a thin hydrophilic layer by processes known per se. Advantageous coatings consist, for example, of TiO₂, ZrO₂ or also other polymers, such as, for example, polymethyl methacrylate.

Particularly advantageous microfine polymer particles for the purposes of the present invention are also obtainable by the process, described in U.S. Pat. No. 4,898,913, for the hydrophilic coating of hydrophobic polymer particles.

It is advantageous to choose the average particle diameter of the microfine polymer particles used to be less than 100 μm, particularly advantageously less than 50 μm. In this connection, it is essentially insignificant in which form (platelets, rods, spherules, etc.) the polymer particles used are present.

In addition, it is advantageous to stabilize the Pickering emulsions according to the invention using modified polysaccharides.

For the purposes of the present invention, modified polysaccharides are, for example, obtainable by reaction of starch with mono-, bi- or polyfunctional reagents or oxidizing agents in reactions which proceed in a largely polymer-analogous manner.

Such reactions are based essentially on modifications of the hydroxyl groups of the polyglucans by etherification, esterification or selective oxidation. This produces, for example, so-called starch ethers and starch esters of the general structural formula

in which R can, for example, be a hydrogen and/or an alkyl and/or an aralkyl radical (in the case of starch ethers) or a hydrogen and/or an organic and/or inorganic acid radical (in the case of starch esters). Starch ethers and starch esters are advantageous, modified polysaccharides for the purposes of the present invention.

Particularly advantageous starch ethers are, for example, those which are obtainable by etherification of starch with tetramethylolacetylenediurea and which are referred to as non-mucilaginous starch (nonswelling starch).

Also particularly advantageous are starch esters and salts thereof, for example the sodium and/or aluminium salts of half-esters of starch which have low degrees of substitution, in particular sodium starch n-octenyl succinate of the structural formula (II) in which R is characterized by the following structure

and which is available, for example, under the trade name Amiogum® 23 from CERESTAR, and aluminium starch octenyl succinates, in particular those available under the trade names Dry Flo® Elite LL and Dry Flo® PC from CERESTAR.

It is advantageous to choose the average particle diameter of the modified polysaccharide used to be less than 20 μm, particularly advantageously less than 15 μm.

The list of given modified polysaccharides which are able to stabilize Pickering emulsions according to the invention is of course not intended to be limiting. For the purposes of the present invention, modified polysaccharides are obtainable in a large number of ways known per se, both of a chemical and a physical nature.

The abovementioned amphiphilic particles are outstandingly suitable both for the stabilization of W/O Pickering emulsions and for the stabilization of O/W Pickering emulsions. Microfine particles according to the invention which advantageously stabilize one of the two emulsion types W/O or O/W in particular are mentioned below.

W/O Pickering Emusions:

The water phase proportion of the W/O Pickering emulsions according to the invention is preferably selected from the range of 0.5 to 75% by weight, based on the total weight of the formulations.

In particular, magnesium silicates (also: talc), for example those obtainable under the trade name Talkum Micron from Grolmann are also advantageous for the stabilization of W/O Pickering emulsions.

O/W Pickering Emulsions

The fatty phase proportion of the O/W Pickering emulsions according to the invention is preferably selected from the range of 0.5 to 75% by weight, based on the total weight of the formulations.

Within the meaning of the present invention, untreated, almost pure pigment particles, for example titanium dioxide pigments, in particular those which are obtainable under the trade name KRONOS® 1171 (TiO₂) from Kronos Titan, are also particularly advantageous for the stabilization of O/W Pickering emulsions.

Within the meaning of the present invention, O/W Pickering emulsions are furthermore particularly advantageously stabilized by metal oxide particles which are coated with aluminium hydroxide and/or silicon dioxide. Advantageous embodiments are, for example, titanium dioxide particles, which are obtainable under the name EUSOLEX® TA from Merck.

It is furthermore advantageous, although not obligatory, to combine the microfine particles according to the invention with further amphiphilic particles which can optionally also contribute to the stabilization of the Pickering emulsions.

Such particles are, for example, titanium dioxide pigments which are coated with octylsilanol, and/or silicon dioxide particles which have a water-repellent treatment on the surface. Suitable silicon dioxide particles are, for example, spherical polyalkylsilsesquioxane particles, such as are mentioned in European Laid-open Specification 0 686 391. Such polyalkyl silsesquioxane particles are obtainable, for example, from Degussa under the trade names Aerosil R972 and Aerosil 200V. Suitable titanium dioxide particles are likewise obtainable from Degussa under the trade name T805.

The Pickering emulsions according to the invention can be used as a base for cosmetic or dermatological formulations. These can have the customary composition and can serve, for example, for the treatment and the care of the skin, as a lipcare product, as a deodorant product and as a make-up or make-up removal product in decorative cosmetics or as a sunscreen preparation. For use, the cosmetic and dermatological preparations according to the invention are applied to the skin in a sufficient amount in the manner customary for cosmetics.

Accordingly, cosmetic or topical dermatological compositions within the meaning of the present invention can be used, depending on their composition, for example, as a skin-protection cream, cleansing milk, sunscreen lotion, nutrient cream, day or night cream etc. It is optionally possible and advantageous to use the compositions according to the invention as a base for pharmaceutical formulations.

The cosmetic and dermatological preparations according to the invention can contain cosmetic auxiliaries, such as are customarily used in such preparations, e.g. preservatives, bactericides, perfumes, substances for preventing foaming, colourants, pigments which have a colouring action, thickeners, emollient, moisturizing and/or humectant substances, fats, oils, waxes or other customary constituents of a cosmetic or dermatological formulation such as alcohols, polyols, polymers, foam stabilizers, electrolytes, organic solvents or silicone derivatives.

Pickering emulsions according to the invention can also contain thickening agents in order to improve the tactile properties of the emulsion.

In particular, the Pickering emulsions according to the invention can also contain antioxidants. According to the invention, all antioxidants suitable or customary for cosmetic and/or dermatological applications can be used as favourable antioxidants.

Advantageously, the antioxidants are selected from the group consisting of amino acids (e.g. glycine, histidine, tyrosine, tryptophan) and their derivatives, imidazoles (e.g. urocanic acid) and their derivatives, peptides, such as D,L-camosine, D-carnosine, L-carnosine and their derivatives (e.g. anserine), carotenoids, carotenes (e.g. α-carotene, β-carotene, lycopene) and their derivatives, chlorogenic acid and its derivatives, lipoic acid and its derivatives (e.g. dihydrolipoic acid), aurothioglucose, propylthiouracil and other thiols (e.g. thioredoxin, glutathione, cysteine, cystine, cystamine and their glycosyl, N-acetyl, methyl, ethyl, propyl, amyl, butyl and lauryl, palmitoyl, oleyl, γ-linoleyl, cholesteryl and glyceryl esters) and their salts, dilauryl thiodipropionate, distearyl thiodipropionate, thiodipropionic acid and its derivatives (esters, ethers, peptides, lipids, nucleotides, nucleosides and salts) and also sulphoximine compounds (e.g. buthionine sulphoximine, homocysteine sulphoximine, buthionine sulphone, penta-, hexa- and heptathionine sulphoximine) in very low tolerable doses (e.g. pmol to μmol/kg), furthermore (metal) chelators (e.g. α-hydroxy fatty acids, palmitic acid, phytic acid, lactoferrin), α-hydroxy acids (e.g. citric acid, lactic acid, malic acid), humic acid, bile acid, bile extracts, bilirubin, biliverdin, EDTA, EGTA and their derivatives, unsaturated fatty acids and their derivatives (e.g. γ-linolenic acid, linoleic acid, oleic acid), folic acid and its derivatives, ubiquinone and ubiquinol and their derivatives, vitamin C and derivatives (e.g. ascorbyl palmitate, Mg ascorbyl phosphate, ascorbyl acetate), tocopherols and derivatives (e.g. vitamin E acetate), vitamin A and derivatives (vitamin A palmitate) and coniferyl benzoate of benzoin, rutic acid and its derivatives, α-glycosylrutin, ferulic acid, furfurylideneglucitol, carnosine, butylhydroxytoluene, butylhydroxyanisole, nordihydroguaiac acid, nordihydroguaiaretic acid, trihydroxybutyrophenone, uric acid and its derivatives, mannose and its derivatives, zinc and its derivatives (e.g. ZnO, ZnSO₄), selenium and its derivatives (e.g. selenomethionine), stilbene and its derivatives (e.g. stilbene oxide, trans-stilbene oxide), and the derivatives which are suitable according to the invention (salts, esters, ethers, sugars, nucleotides, nucleosides, peptides and lipids) of these said active compounds.

The amount of the abovementioned antioxidants (one or more compounds) in the preparations according to the invention is preferably 0.001 to 30% by weight, particularly preferably 0.05 to 20% by weight, in particular 1 to 10% by weight, based on the total weight of the preparation.

If vitamin E and/or its derivatives are the antioxidant(s), it is advantageous to select their respective concentrations from the range of 0.001–10% by weight, based on the total weight of the formulation.

If vitamin A, or vitamin A derivatives, or carotenes or their derivatives are the antioxidant(s), it is advantageous to select their respective concentrations from the range of 0.001–10% by weight, based on the total weight of the formulation.

Cosmetic and dermatological preparations which are present in the form of a sunscreen composition are also favourable. Preferably, these contain at least one UV-A filter substance and/or at least one UV-B filter substance and/or at least one further inorganic pigment from the group consisting of the oxides of iron, zirconium, silicon, manganese, aluminium, cerium and mixtures thereof and modifications in which the oxides are the active agents.

However, it is also advantageous within the meaning of the present invention to make available those cosmetic and dermatological preparations whose main purpose is not protection from sunlight, but which nevertheless contain UV protection substances. Thus, UV-A and UV-B filter substances are usually incorporated, for example, in day creams.

Advantageously, preparations according to the invention can contain substances which absorb UV radiation in the UV-B range, the total amount of the filter substances being, for example, 0.1% by weight to 30% by weight, preferably 0.5 to 10% by weight, in particular 1.0 to 6.0% by weight, based on the total weight of the preparations, in order to make available cosmetic preparations which protect the hair or the skin from the entire range of ultraviolet radiation.

If the emulsions according to the invention contain UV-B filter substances, these can be oil-soluble or water-soluble. Advantageous oil-soluble UV-B filters according to the invention are, for example:

-   -   3-benzylidenecamphor derivatives, preferably         3-(4-methylbenzylidene)camphor, 3-benzylidenecamphor;     -   4-aminobenzoic acid derivatives, preferably 2-ethylhexyl         4-dimethylaminobenzoate, amyl 4-dimethylaminobenzoate;     -   esters of cinnamic acid, preferably 2-ethylhexyl         4-methoxycinnamate, isopentyl 4-methoxycinnamate;     -   esters of salicylic acid, preferably 2-ethylhexyl salicylate,         4-isopropylbenzyl salicylate, homomenthyl salicylate,     -   derivatives of benzophenone, preferably         2-hydroxy-4-methoxybenzophenone,         2-hydroxy-4-methoxy-4′-methylbenzophenone,         2,2′-dihydroxy-4-methoxybenzophenone;     -   esters of benzalmalonic acid, preferably 2-ethylhexyl         4-methoxybenzalmalonate,     -   triazine derivatives which are symmetrical with respect to the         C₃ axis of the triazine parent structure, preferably         tris-2-ethylhexyl         4,4′,4″-(1,3,5-triazine-2,4,6,-triyltriimino)trisbenzoate,     -   benzotriazole derivatives, preferably         2,2′-methylene-bis(6-(2H-benzotriazol-2-yl)-4-(1,1,3,3,-tetramethylbutyl)phenol)     -   and UV filters bonded to polymers.

Advantageous water-soluble UV-B filters are, for example:

-   -   salts of 2-phenylbenzimidazole-5-sulphonic acid such as its         sodium salt, potassium salt or its triethanolammonium salt, and         the suphonic acid itself;     -   sulphonic acid derivatives of benzophenones, preferably         2-hydroxy-4-methoxybenzophenone-5-sulphonic acid and its salts;     -   sulphonic acid derivatives of 3-benzylidenecamphor, such as, for         example, 4-(2-oxo-3-bornylidenemethyl)benzenesulphonic acid,         2-methyl-5-(2-oxo-3-bornylidenemethyl)sulphonic acid and their         salts.

The list of the said UV-B filters which can be used in the Pickering emulsions according to the invention should, of course, be non-limiting.

It can also be advantageous to use UV-A filters which hitherto have customarily been contained in cosmetic preparations in Pickering emulsions according to the invention. These substances are preferably derivatives of dibenzoylmethane, in particular 1-(4′-tert-butylphenyl)-3-(4′-methoxyphenyl)propane-1,3-dione and 1-phenyl-3-(4′-isopropylphenyl)-propane-1,3-dione.

Other advantageous UV-A filter substances are phenylene-1,4-bis(2-benzimidazyl)-3,3′-5,5′-tetrasulphonic acid:

and its salts, particularly the corresponding sodium, potassium or triethanolammonium salts, in particular the bis-sodium salt of phenylene-1,4-bis(2-benzimidazyl)-3, 3′-5,5′-tetrasulphonic acid:

and 1,4-di(2-oxo-10-sulfo-3-bornylidenemethyl)benzene and salts thereof (particularly the corresponding 10-sulfato compounds, in particular the corresponding sodium, potassium or triethanolammonium salt), which is also referred to as benzene-1,4-di(2-oxo-3-bornylidenemethyl-10-sulphonic acid) and is characterized by the following structure:

Preparations which contain UV-A filters are also a subject of the invention. The amounts used for the UV-B combination can be employed.

Preparations according to the invention can also be advantageously used as bases for cosmetic deodorants and antiperspirants, so that a particular embodiment of the present invention relates to Pickering emulsions as bases for cosmetic deodorants.

Cosmetic deodorants are used to control body odour which arises when fresh perspiration, which is in itself odourless, is decomposed by microorganisms. Customary cosmetic deodorants are based on various modes of action.

In antiperspirants, astringents, mainly aluminium salts, such as aluminium hydroxychloride (aluminium chlorohydrate), reduce the formation of perspiration.

The use of antimicrobial substances in cosmetic deodorants can reduce the bacterial flora of the skin. In an ideal situation, only the microorganisms which cause the odour should be effectively reduced. The flow of perspiration itself is not influenced as a result, and in ideal circumstances, only microbial decomposition of perspiration is stopped temporarily.

The combination of astringents and antimicrobial active substances in one and the same composition is also common.

All active ingredients common for deodorants or antiperspirants can advantageously be used, for example odour concealers, such as customary perfume constituents, odour absorbers, for example the phyllosilicates described in Laid-open Patent Specification DE 40 09 347, of these in particular montmorillonite, kaolinite, illite, beidellite, nontronite, saponite, hectorite, bentonite, smectite, and also, for example, zinc salts of ricinoleic acid. Antibacterial agents are also suitable to be incorporated into the novel W/O emulsion sticks. Advantageous substances are, for example, 2,4,4′-trichloro-2′-hydroxy diphenyl ether (Irgasan), 1,6-di(4-chlorophenylbiguanido)hexane (chlorhexidine), 3,4,4′-trichlorocarbanilide, quaternary ammonium compounds, oil of cloves, mint oil, thyme oil, triethyl citrate, farnesol (3,7,11-trimethyl-2,6,10-dodecatrien-1-ol) and also the active ingredients or active ingredient combinations described in the Laid-open Patent Specifications DE-A-37 40 186, DE-A-39 38 140, DE-A-42 04 321, DE-A-42 29 707, DE-A-43 09 372, DE-A44 11 664, DE-A-195 41 967, DE-A-195 43 695, DE-A-195 43 696, DE-A-195 47 160, DE-A-196 02 108, DE-A-196 02 110, DE-A-196 02 111, DE-A-196 31 003, DE-A-196 31 004 and DE-A-196 34 019, and the Patent SSpecifications DE-42 29 737, DE-42 37 081, DE-43 24 219, DE-44 29 467, DE-44 23 410 and DE-195 16 705. Sodium hydrogencarbonate can also be used advantageously.

The list of specified active ingredients and active ingredient combinations is of course not intended to be limiting.

The amount of antiperspirant active ingredients or deodorants (one or more compounds) in the preparations is preferably from 0.01 to 30% by weight, particularly preferably from 0.1 to 20% by weight, in particular 1–10% by weight, based on the total weight of the preparation.

The examples below serve to illustrate the present invention without limiting it. The numerical values in the examples are percentages by weight, based on the total weight of the respective preparations.

EXAMPLES

Examples: 1 2 3 4 5 6 W/O W/O W/O O/W O/W O/W Titanium dioxide (Eusolex 2 4 6 3 5 2 T2000) Zinc oxide 5 4 4 Titanium dioxide (Titandioxid 2 T805) Silica (Aerosil R972) 1 0.5 Talc (Talkum Micron) 0.5 Boron nitride 2 Sodium maize starch 0.5 1 n-octenylsuccinate Hydroxystearyl 2 2 hydroxystearate (Elfacos C26) C_(20–40)-alkyl stearate 1 1 (Kesterwachs K82) C_(16–38)-alkylhydroxystearolyl 2 3 stearate (Kesterwachs K80P) Behenoxy dimethicone (Abil 5 5 Wax 2440) Polyisobutene (Rewopal PIB 5 1000) Caprylic/capric triglyceride 5 5 5 20 20 20 Octyldodecanol 5 5 15 15 Mineral oil 10 10 20 Butylene glycol 10 10 20 7 caprylate/caprate C_(12–15)-alkyl benzoate 10 10 10 5 15 Dimethicone 2 3 Dicaprylyl ether (Cetiol OE) 5 Hydrogenated polyisobutene 2 (Polysynian) Methylbenzylidenecamphor 3 4 Octyltriazone 1 4 Dibenzoylmethane 2 2 Dioctylbutamidotriazone 2 (UVASORB HEB) Preservative 0.5 0.5 0.5 0.5 0.5 0.5 Glycerol 5 10 3 5 5 5 Biosaccharide gel (Fucogel 5 1000) Hyaluronic acid 0.5 NaCl 1 1 0.5 0.5 MgSO₄ 0.5 Phenylbenzimidazole- 1 2 sulphonic acid Carbomer (Carbopol 981) 0.1 Xanthan gum 0.3 Cellulose gum (Natrosol Plus 0.05 330 CS) NaOH 45% strength solution 0.3 0.1 0.7 in water EDTA solution 1 1 Water ad ad ad ad ad ad 100 100 100 100 100 100 

1. Pickering emulsions, which are finely disperse water-in-oil or oil-in-water systems, comprising (1) an oil phase, (2) an aqueous phase, (3) microfine particles which are metal oxides which (a) have an average particle size of less than 200 nm, which (b) display both hydrophilic and lipophilic properties, (amphiphilic character), and are dispersible both in water and in oil and which (c) have optionally been coated on the surface, (4) at least one electrolyte and (5) being emulsifier-free.
 2. Pickering emulsions according to claim 1, wherein said Pickering emulsions are water-in-oil emulsions.
 3. Pickering emulsions according to claim 1, wherein the content of the particles used is between 0.1% by weight and 30% by weight, based on the total weight of the Pickering emulsions.
 4. Pickering emulsions according to claim 1, wherein the particle diameter of the particles used is between 5 nm and 100 nm.
 5. Pickering emulsions according to claim 1, wherein the particles used have been surface-treated to repel water, where the amphiphilic character of the particles is formed or retained.
 6. Water-in-oil Pickering emulsions according to claim 1, wherein the total amount of one or more electrolytes in the emulsion is less than 5.0% by weight, based on the total weight of the Pickering emulsions.
 7. Pickering emulsions according to claim 1, wherein the electrolyte(s) is/are chosen from the group of potassium chloride, sodium chloride, magnesium sulphate and zinc sulphate.
 8. Pickering emulsions according to claim 1, wherein the electrolyte(s) is/are selected from the group which is formed from water-soluble UV filter substances which carry one or more sulphonic acid groups or sulphonate groups in their molecular structure, and their salts.
 9. Pickering emulsions according to claim 1, wherein said emulsions comprise auxiliaries which can contribute to reducing or preventing a dull or dry feel on the skin following their application.
 10. The water-in-oil Pickering emulsions of claim 6, wherein the total amount of one or more electrolytes is between 0.5 and 2.0% by weight, based on the total weight of the emulsions.
 11. A method of caring for skin, said method comprising applying to skin Pickering emulsions according to any one of claims 1,2,3,4, or 5–10.
 12. A method of stabilizing cosmetic or dermatological Pickering emulsions which are comprised of: (1) an oil phase, (2) an aqueous phase, (3) microfine particles which are metal oxides which (a) have an average particle size of less than 200 nm, which (b) display both hydrophilic and lipophilic properties, (amphiphilic character), and are dispersible both in water and in oil and which (c) have optionally been coated on the surface, and which are emulsifier-free which comprises adding at least one electrolyte to said Pickering emulsions. 